Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$129.88	3.758%	$134.7609	$134.76	$134.75	$134.80
Purchase #2	$170.33	3.498%	$176.2881	$176.29	$176.30	$176.30
Purchase #3	$186.66	13.338%	$211.5567	$211.56	$211.55	$211.60
Purchase #4	$63.64	10.386%	$70.2497	$70.25	$70.25	$70.20
Purchase #5	$168.92	11.620%	$188.5485	$188.55	$188.55	$188.50
Purchase #6	$54.75	11.689%	$61.1497	$61.15	$61.15	$61.10
Purchase #7	$43.51	4.788%	$45.5933	$45.59	$45.60	$45.60
7 purchase totals =	$817.69		$888.1469	$888.15	$888.15	$888.10